Mexican drug smugglers are using an ancient invention as a new way to move marijuana across the border into the United States.

The discovery of two 'drug catapults' in the Mexican state of Sonora marks the latest twist in the cat-and-mouse game traffickers play with authorities.

US National Guard troops operating a remote surveillance system at the Naco Border Patrol Station in Arizona observed several people preparing a catapult and launching packages over the fence late last week.

A Mexican army officer said the three-metre tall catapult was found about 20 metres from the US border on a trailer towed by an off-road vehicle.

The officer said the catapult was capable of launching two kilograms of marijuana at a time. He says soldiers seized 16 kilograms of cannabis, the vehicle and the catapult.

The smugglers left before they could be captured.

A second catapult was discovered the following day in nearby Agua Prieta, another border town. An anonymous tip led soldiers to the scene.

Mexican officials say it is the first time they have seen this smuggling method used by local traffickers.

Traffickers have previously used planes, tunnels, vehicles, boats and couriers to smuggle drugs into the United States. Colombian drug traffickers have even used homemade submarines.